Telescopic screw



Nov. 8, 1932. T. TRECKER TELESCOPIC SCREW Filed May 24, 1928 /V/VV/f ///////////V V m e f 9 .a Mm .I

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lNvENToR Patented Nov. 8, 1932 UNITED snare i-FICE THEODORE TRECKER, kF MILWAUKEE, `WISCONSIN, ASSIGNOR TO KEARNEY do TRECKER CORPORATION, OF WEST ALLIS, WISCONSIN TRI-,Escono SCREW Application led May 24, 1928. Serial No. 280,166.

This invention relates to an improved construction for telescopic screws, particularly for use in machine tools.

A purpose is to prevent the tight seating of shoulders or abutments required for limiting the relative axial movement of different portions of such screws.

A further. purpose is generally to simplify and improve the construction and operation 1o of such screws, and still other purposes will be apparent from this specification.

The invention consists in the arrangement and combination of parts here-in illustrated, described and claimed and in such modifica .tions of the structure illustrated as may be the equivalent of the structure claimed.

In the drawing, Fig. 1 is a vertical section through a telescopic screw in which the inventionis incorporated, the screw being here shown associated with the knee and column of a milling machine for the purpose of relative vertical movement therebetween.

Fig. 2 is a horizontal section along line 2 2 of Fig. l.

The machine column l, of which only a portion is shown is provided with suitable slides for guiding afknee 2 for vertical movement. Such movement is brought about by means of a hand crank (not shown) applied to the 3o squared end 3 of a shaft 4 or by power applied to a gear 5 fixed on a shaft 6.

An inner screw 7 is journaled in a bearing 8 fixed with the knee and is prevented from axial movement relative thereto by means "including for the one direction a thrust bearing 9 positioned between suitable shoulders or abutments respectively on a bevel gear 10 and bearing 8, and for the other direction a nut 11 threaded on the end of the screw to retain a 4U Ithrust washer 12 which seats against an abutment at the other end of bearing 8.

The inner screw portion 7 is in threaded engagement with an axial bore 13 forming a nut in an outer screw portion 14, which in turn is in threaded engagement with a nut V15 fixed in an upwardly extended stump 16 fixed on the base of column 1. v

The mechanism just described constitutes Aa telescopic screw arrangement commonly used for the movement of milling machine knees, where the nature of the machine is such that plain screws giving sufficient range of movement would, at certain points of their movement project below the lower plane of y the column base. Y

The bevel gear 10 and screws 7 and14 are moved from shaft 4 Yby the means ofa bevel gear 17 fixed on shaft 4 and engaging gear l0; and are moved from shaft 6 by the means of a bevel gear 18 engaging gear 10.

The power mechanism (not shown) for-4 movement of gear 5 ordinarily includes a slow orfeed transmission and a fast transmission for quick knee movement.

.At-the end of screw 7 is fixed a collar 19 oai which will at times strike or seat against a shoulder 20 in the enlarged bore 2l through which the collar moves. The one end of screw 14 has a head portion 22 fixed thereon which, unless prevented, will at times strike or seat 76:3' against the upper face of nut 15 and at other times against the lower face of bevel gear 10. The otherend of screw 14 has fixed thereon a collar 23 which will at times strike against' the lower face of nut 15. v

Some such construction is necessary in an extensible screw, in order that the different screw members thereof may each be forced at some point ofthe travel to take up a rotational and axial movement before `the otherv 80` v screw member disengages. from its nut, but the construction thus far described'` unless modified has disadvantages or objections in that, whena. screw is provided with a collar or head which is forced by the screw rotation 8551 toseatagainst the end of the nut, a wedging action takes place owing to the relatively small angle of the screw thread and ina telescopic screw, where different shoulders or collars operate `alternatelyin dierent direc- 903- tions of movement of the parts the force of such wedging action may be cumulative as follows: l

During a first movement in one direction, a given shoulder wedges moderately, during a first reverse movement, an opposite shoulder also wedges moderately. Such forces are moderate because the only work performed is'to start the other screwr member against or-r` dinary screw friction and inertia. But onV '10 of screw 14 is provided with a peripheral.

projection or lug 24, the opposite faces 24a and 24?) of which form abutments. The screws shown have right hand thread, whereby abutment 24a is contacted at the lower point of the travel of screw 14 by a lug or abutment 25 fixed with nut l5, and abut-ment 246 is contacted at the lower point of the relative movement of screw 7 by a lug or abutment 26 fixed with gear l0. ln each instance, the relationship of the parts is such that as the lug 24: approaches the one or the other of lugs 25-26, lug 24 will at certain revolution barelyclear the top of the other lug but at the next succeeding revolution will have advancedaxially suii'iciently to give a substantial bearing against` the face 2a@ or 24?).

When such lug contact occurs the relative rotation and hence the relative axial movement of head 22 is checked and the end faces thereof never seat. lt is obvious that no wedging action such as mentioned above can ,be set up by stops which act directly against the'rotational movement instead of the axial movement, and since all the stops contacted during downward movement of the knee, that is tosay in the one direction of screw movement, are non-wedging, the cumulative result mentioned above can never occur.

It is contemplated Vand obviously practicable to apply similar non-wedging stops, when necessary, to both directions of screw movement.

What is claimed:

1. In a machine tool having relatively movable supports and a telescopic screw for movement of said supports, said screw havin@ co-axial inner and outer relatively rotatab e and axially movable members, the combination of a rst stop for limiting the axial movement of one of said members relative to the other, and a second stop for limiting the axial movement of said other member relative vto one of said supports, each of said stops including contact portions Vrelatively rotatable into a position of mutually opposed thrust transverse to the axis of rotation,

whereby to avoid substantially all thrust between the stop portions in the direction of said axis.

2. In a machine tool having relatively reciprocatory supports and a telescopic screw for movement of said supports, said screw having co-axial inner and outer relatively rotatable and axially movable members, the combination of a plurality of stops collectively defining the limits of axial movement of both said members in one direction of support movement, each of said stops including contact portions relatively rotatable into a position of mutually opposed thrust transverse V to the axis of rotation, whereby to substantially avoid axial thrust between any7 stop portions during at' least one direction of support movement.

3. In a milling machine the combination ofa column having a base portion, a knee guided. on said column for vertical movement, a irst screw journaled in said knee and axially' movable therewith, a second screw having a threaded bore engaging said first screw, a nut iixed with said column base portion and engaging said secon-d screw, means associated with said knee for rotation` of said first screw, and means for rotation o said second screw including contact memei's respectively associatedwith the differont screws, one of said members being rotatable with said lirst screw toV thrust against the other or said membersin a direction transverse to the axis of rotation whereby to substantially avoid thrust between said .ieinbers in the direction of said axis.

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